JPH06236851A - Manufacture of n-type cubic boron nitride semiconductor - Google Patents

Abstract

PURPOSE:To provide a method of manufacturing an N-type cubic boron nitride semiconductor, wherein a large N-type cubic baron nitride semiconductor thin film excellent in crystallinity and small in residual impurities can be obtained through a vapor composition method as it is controlled in the amount of dopant. CONSTITUTION:An N-type cubic boron nitride semiconductor thin film is formed through such a method that at least either of Si hydride or Si halogenide is added in gas phase to material gas introduced into a vacuum chamber 1, and a mixture gas is activated into plasma, which is fed to the surface of a heated substrate 2. Thus, an N-type cubic boron nitride crystal thin film is deposited as it is doped with Si as N-type impurity element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing an n-type cubic boron nitride semiconductor thin film used for heat-resistant devices, environment-resistant devices and the like, and more particularly to a synthesizing method using a plasma CVD method.

[0002]

2. Description of the Related Art Boron nitride is a compound BN of boron and nitrogen, including a hexagonal lattice layered compound (hBN), high pressure cubic boron nitride (cBN), and wurtzite hexagonal (wBN). Four crystal phases of rhombohedral (rBN) have been reported.

Among them, cubic boron nitride (cBN) has a zinc blende type crystal structure and exhibits hardness second only to diamond, and like diamond, it has heat resistance, oxidation resistance, environment resistance and heat conduction characteristics. It has excellent characteristics. The band gap is also very wide.

Conventionally, cubic boron nitride is industrially used in the same manner as diamond by using an ultrahigh pressure and ultrahigh temperature generator to produce powder of hexagonal boron nitride at 50 to 60 Kbar and 1200 ° C.
It is synthesized under the above high pressure and high temperature conditions.

Further, until now, a small amount of n has been used in the high pressure synthesis method.
It is known that an n-type cubic boron nitride semiconductor crystal having conductivity can be obtained by adding a type impurity element to BN raw material powder and growing a crystal.

[0006]

However, there are the following problems in the synthesis of the n-type cubic boron nitride semiconductor by the above-mentioned conventional high-pressure synthesis method.

First, an ultrahigh pressure synthesizer for generating a high pressure of tens of thousands of atmospheres is extremely expensive, and the internal volume of the reaction section of the apparatus is limited. Therefore, it is extremely difficult to grow a cubic boron nitride crystal in a large area, and this is a major cause that the cubic boron nitride crystal cannot be supplied at a low cost.

Secondly, in the high-pressure synthesis method, since the impurity introduction element is added to the hexagonal boron nitride powder before crystal synthesis in advance, the controllability of the doping amount of the introduction element is extremely poor and There is a problem that the impurity distribution is likely to be non-uniform in the formed crystal.

Thirdly, in the high pressure synthesis method, Li ₃ N or MgB containing an alkali metal or an alkaline earth metal element in hexagonal boron nitride powder is used in order to lower the reaction temperature.
Since a compound such as N ₃ was added as a catalyst, it was very difficult to avoid mixing metallic elements such as Li and Mg as impurities into the cubic boron nitride crystal.

As described above, in practice, it is almost impossible to synthesize an n-type cubic boron nitride semiconductor composed of a large single crystal having a small amount of residual impurities, which can be applied to a semiconductor material by a high-pressure synthesis method. It was impossible.

The present invention solves the above-mentioned conventional problems and provides a large-sized n-type cubic boron nitride semiconductor thin film having a small amount of residual impurities and excellent crystallinity while controlling the doping amount by vapor phase synthesis. An object is to provide a method for producing an n-type cubic boron nitride semiconductor that can be obtained.

[0012]

In the same way as for diamond, cubic boron nitride has recently been actively studied and developed for a vapor phase synthesis method in which it is precipitated from a vapor phase on a substrate heated.

Examples of the methods currently attempted include an ion plating method using metal boron as a boron source, an ionization vapor deposition method, an IVD method and a sputtering method.

Further, gas is used as a boron source and a nitrogen source, and electric power of high frequency, microwave, etc. is externally applied to the raw material gas to excite a plasma state, and cubic boron nitride is heated on the heated and held substrate. Plasma CVD method to deposit,
Alternatively, there is also known an ECR plasma CVD method in which a microwave is applied to excite ECR plasma after applying a magnetic field value that causes an electron cyclotron resonance state to deposit cubic boron nitride on a substrate that has been heated and held. .

Therefore, the inventors of the present invention are known to be able to obtain a cubic boron nitride crystal having a relatively high crystallinity and a high purity among the vapor phase synthesis methods that have been attempted so far. Method, in particular, ECR plasma CVD method, in order to synthesize a large-sized n-type cubic boron nitride semiconductor excellent in crystallinity with little residual impurities, earnestly studied on selection of n-type impurity element and introduction method thereof. result,
At least one of a hydride and a halide of silicon (Si), or at least one of a hydride and a halide of sulfur (S) is used as an introduction element supply gas, and a gas containing a boron atom and a gas containing a nitrogen atom are main components. It was found that an n-type cubic boron nitride semiconductor thin film can be formed on the surface of a substrate while controlling the doping of an n-type impurity element into a growing cubic boron nitride crystal by adding it to a raw material gas. The invention was completed.

That is, in the method for producing an n-type cubic boron nitride semiconductor according to the first aspect of the present invention, a raw material gas containing a boron atom-containing gas and a nitrogen atom-containing gas as main components is introduced into the reaction system to produce a raw material gas. In a plasma CVD method in which plasma generated by activation is supplied to a heated substrate surface to deposit cubic boron nitride, at least one of a hydride and a halide of silicon (Si) is vaporized in a source gas. Is added to form an n-type cubic boron nitride semiconductor thin film on the surface of the substrate while doping the n-type impurity element.

Further, in the method for producing an n-type cubic boron nitride semiconductor according to the second aspect of the invention, a raw material gas containing a boron atom-containing gas and a nitrogen atom-containing gas as main components is introduced into the reaction system to produce a raw material gas. In a plasma CVD method in which plasma generated by activation is supplied to a heated substrate surface to deposit cubic boron nitride, at least one of a hydride and a halide of sulfur (S) is vaporized in a source gas. Is added to form an n-type cubic boron nitride semiconductor thin film on the surface of the substrate while doping the n-type impurity element.

In the first invention, the hydride of silicon (Si) added to the source gas in a vapor phase is Si
H ₄ , Si ₂ H _{6 and the} like are used as silicon (Si) halides such as SiF ₄ , SiF ₂ H ₂ , SiCl ₄ , and SiCl ₄ .
₂ H _{2 and the} like can be preferably used.

Further, in the second invention, H ₂ is used as the hydride of sulfur (S) added to the raw material gas in the vapor phase state.
As S or the like, SF ₆ or the like can be preferably used as the sulfur (S) halide.

The silicon hydrides and halides or the sulfur hydrides and halides used in the first and second inventions are generally readily available as commercial high-pressure liquid gases.

When silicon is doped as the n-type impurity in the first invention, either a hydride or a halide of silicon may be used alone, or both may be used in combination.

In the second aspect of the invention, when sulfur is doped as the n-type impurity element, either a hydride or a halide of sulfur may be used alone, or both may be used in combination. .

In the present invention, the doping amount of the n-type impurity element can be adjusted with good controllability by changing the flow rate ratio of the introduction element supply gas added to the source gas. At this time, the concentration of addition of the n-type impurity element atom to the boron atom in the source gas during film formation is preferably 1 ppm or more and 5% or less, and 10 ppm or more and 5000 ppm
The following is more preferable.

Since cubic boron nitride is originally a substance having an extremely high insulating property, if the concentration of addition of n-type impurity element atoms to boron atoms is less than 1 ppm, the electrical conductivity of cubic boron nitride is low even if it is added. Remains suppressed,
It is not possible to produce cubic boron nitride with low electrical resistance. On the other hand, when the concentration of addition of the n-type impurity element atom to the boron atom exceeds 5%, the n-type impurity element atom combines with the boron atom and the nitrogen atom in the cubic boron nitride crystal to form another compound such as SiB _6. It is not preferable because it may occur.

In the present invention, it is preferable to use diborane or boron trichloride as the source of the boron atom-containing gas, and it is preferable to use nitrogen gas or ammonia as the source of the nitrogen atom-containing gas. As the raw material gas introduced into the reaction system, hydrogen or an inert gas represented by a rare gas such as Ar, Kr, or Xe may be mixed and used in addition to the above gases.

Further, in the plasma CVD method, it is not particularly necessary to heat, but in order to improve the crystallinity, it is preferable that the surface temperature of the substrate is kept warm in the range of 800 to 1200 ° C.

The pressure in the reaction system is 1 × 10 ^-6 Torr to 4
The plasma can be stably maintained in a very wide range of × 10 ² Torr and cubic boron nitride can be deposited, but the deposition rate becomes extremely small when the pressure is low. 10 ^-5 Torr to 1 × 10 ²
The range of Torr is preferable.

[0028]

In the first invention, silicon (Si) is used as the n-type impurity element.
In the second invention, sulfur (S) is selected as the n-type impurity element to manufacture an n-type cubic boron nitride semiconductor.

In the method for manufacturing an n-type cubic boron nitride semiconductor according to the first aspect of the present invention, as a method for doping an n-type impurity element into a cubic boron nitride crystal during growth in a plasma CVD method, silicon hydride and halogen are used. A method is used in which at least one of the compounds is added in a vapor phase state to a raw material gas containing a boron atom-containing gas and a nitrogen atom-containing gas as main components.

In the first aspect of the present invention, by using at least one of silicon hydride and halide as a source of the n-type impurity element, the n-type cubic boron nitride having extremely small residual impurities and excellent conductivity is used. The reason why the semiconductor crystal thin film can be formed is considered to be mainly due to the following reasons.

The above-mentioned silicon compound is composed only of the n-type impurity element (Si) to be doped and hydrogen or a gas atom of a halogen group. Therefore, the plasma C
In the VD method, one of silicon hydride and halide added to the source gas is dissociated and excited by plasma discharge together with the source gas and activated into radicals or positively charged ions. It is considered that the Si atoms thus excited and ionized are efficiently incorporated into the cubic boron nitride crystal grown by the reaction of the heated substrate surface. On the other hand, excited hydrogen or halogen group gas atoms are also taken into the cBN crystal, but it is considered that these elements do not form a new electronic state relating to crystal conductivity, that is, a shallow impurity level.

Therefore, the impurities other than the n-type impurity element which increase the conductivity are mixed into the cubic boron nitride crystal, which is suppressed to a very small extent, and an n-type cubic boron nitride semiconductor crystal having excellent conductivity can be obtained. .

According to the first aspect of the invention, the n-type impurity element is doped into the cubic boron nitride crystal by a predetermined amount of the impurity element powder in the BN raw material powder before the crystal synthesis as in the high pressure synthesis method. Instead of adding it, the flow rate ratio of at least one of the hydride and the halide of silicon in the vapor phase to the raw material gas to be introduced into the reaction system along with the formation of the cubic boron nitride thin film by vapor phase synthesis. Since it can be adjusted appropriately, the n-type impurity element is controlled in the cubic boron nitride crystal while controlling the doping amount.
It is possible to synthesize a large-sized n-type cubic boron nitride semiconductor into which a type impurity element is uniformly introduced.

In the method for manufacturing an n-type cubic boron nitride semiconductor according to the second aspect of the invention, as a method for doping an n-type impurity element into a cubic boron nitride crystal during growth in plasma CVD, sulfur hydride and halogen are used. A method is used in which at least one of the compounds is added in a vapor phase state to a raw material gas containing a boron atom-containing gas and a nitrogen atom-containing gas as main components.

In the second invention, by using at least one of a hydride and a halide of sulfur as a source of the n-type impurity element, an n-type cubic boron nitride having extremely small residual impurities and excellent conductivity is provided. The reason why the semiconductor crystal thin film can be formed is considered to be mainly due to the following reasons.

The above-mentioned sulfur compound is composed only of the n-type impurity element (S) to be doped and hydrogen or a gas atom of the halogen group. Therefore, the plasma CV
In the D method, either the hydride or the halide of sulfur added to the raw material gas is dissociated and excited by plasma discharge together with the raw material gas to be activated into radicals or positively charged ions. It is considered that the thus excited and ionized S atoms are efficiently incorporated into the cubic boron nitride crystal grown by the surface reaction of the heated gas. On the other hand, excited hydrogen or halogen group gas atoms are also taken into the cBN crystal, but it is considered that these elements do not form a new electronic state relating to crystal conductivity, that is, a shallow impurity level.

Therefore, the impurities other than the n-type impurity element which increase the conductivity are suppressed in the cubic boron nitride crystal, and the n-type cubic boron nitride semiconductor crystal having excellent conductivity can be obtained. .

According to the second aspect of the invention, the n-type impurity element is doped into the cubic boron nitride crystal by a predetermined amount of the impurity element powder in the BN raw material powder before the crystal synthesis as in the high pressure synthesis method. Rather than adding it in advance, the inflow ratio of at least one of sulfur hydride and halide in the vapor phase to the raw material gas introduced into the reaction system in conjunction with the formation of the cubic boron nitride thin film by vapor phase synthesis Since it can be adjusted appropriately, the n-type impurity element is controlled in the cubic boron nitride crystal while controlling the doping amount.
It is possible to synthesize a large-sized n-type cubic boron nitride semiconductor in which the type impurities are uniformly introduced.

[0039]

EXAMPLES Examples according to the present invention will be described below. However, the present invention is not limited to the following examples.

Example 1 FIG. 1 shows the ECR plasma CVD used in this example.
It is a figure which shows the structure of an apparatus typically. Based on FIG.
The ECR plasma CVD apparatus will be described.

An electromagnetic coil 8 is provided on the side of the ECR plasma chamber 7.
Is provided, and the vacuum chamber 1 is provided so as to communicate with the ECR plasma chamber 7 via the isolation wall. In the vacuum chamber 1, a substrate holder 4 for fixing the substrate is provided at a position 10 cm away from the opening 10 of the ECR plasma chamber 7. A high frequency voltage source 5 and a direct current source 6 for applying a high frequency bias voltage to the substrate are connected to the substrate holder 4. In addition, a heater 3 for heating the substrate is provided near the substrate holder 4,
Substrate heating and bias application can be used together. A sufficiently cleaned substrate having a size of about 1 cm × 1 cm is placed on the substrate holder 4.

The operation of synthesizing a cubic boron nitride thin film using the apparatus having the above structure will be described.

First, the substrate 2 made of a high-pressure synthetic diamond single crystal having a plane orientation (100) is placed on the substrate holder 4. After evacuation by a vacuum pump (not shown) until the atmospheric pressure in the vacuum chamber 1 became 10 ⁻⁷ Torr or less, hydrogen gas was introduced into the vacuum chamber 1 at 10 sccm. Next, by energizing the electromagnetic coil 8, the ECR plasma chamber 7
A magnetic field of about 875 G was generated inside. After applying a magnetic field value that brings the electron cyclotron resonance state in this way, the substrate 2 in the vacuum chamber 1 is heated to 800 ° C., and a microwave 11 of 300 W is introduced into the vacuum chamber 1
CR high density plasma was generated. At this time, a high frequency bias voltage was simultaneously applied to the substrate 2 so that the self-bias value would be −75V. In this state, the surface of the substrate 2 was etched with hydrogen plasma for 10 minutes, and then B ₂ H ₆ gas was added for 1 s.
ccm, 1 sccm of N ₂ gas, 20 scc of Ar gas
m, and SiH ₄ gas was introduced into the vacuum chamber 1 at 0.001 sccm.

In this example, the B ₂ H ₆ gas and the SiH ₄ gas used were diluted with Ar gas.

The source gas and the SiH ₄ gas are decomposed by the ions extracted from the ECR plasma chamber 7 into the vacuum chamber 1, and the chemical species generated from the source gas and the SiH ₄ gas are supplied onto the substrate 2 to about 30. Film formation was performed for a minute.

After the film synthesis, the film obtained on the substrate 2 was examined by infrared absorption spectroscopy and X-ray diffraction, and it was confirmed that the film was a cubic boron nitride single-phase thin film.

When the composition ratio of elements in the thin film was analyzed by the secondary ion gravimetric analysis method, it was found that the ratio of silicon (Si) atoms to boron (B) atoms was 900 ppm.

When the activation energy of the specific resistance and electric resistance of the obtained thin film was examined, the specific resistance was 1 × 10 ^-1 Ωc.
m was confirmed to be an n-type semiconductor.

Example 2 A cubic boron nitride thin film is synthesized using the same ECR plasma CVD apparatus as in Example 1. However, in this example, SiF ₄ gas was used instead of SiH ₄ gas. Therefore, in the present embodiment, after plasma etching, B ₂ H ₆ gas was added at 1 sccm and N ₂
Gas 1 sccm, Ar gas 20 sccm, S
iF ₄ gas was introduced into the vacuum chamber 1 at a rate of 0.0005 sccm, and film formation was performed at a substrate temperature of 800 ° C. for 30 minutes.

After the film synthesis, the film obtained on the substrate 2 was examined by infrared absorption spectroscopy and X-ray diffraction, and it was confirmed that the film was a cubic boron nitride single-phase thin film.

The composition ratio of elements in the thin film was analyzed by secondary ion gravimetric analysis, and it was found that the ratio of silicon (Si) atoms to boron (B) atoms was 500 ppm.

When the activation energy of the specific resistance and electric resistance of the obtained thin film was examined, the specific resistance was 3 × 10 ⁻¹ Ωc.
m was confirmed to be an n-type semiconductor.

Example 3 A cubic boron nitride thin film is synthesized using the same ECR plasma CVD apparatus as in Example 1.

However, in this embodiment, SiH_FourFor gas
Instead of Si₂H₆Gas was used. did
Therefore, in this embodiment, after plasma etching, B₂H
₆Gas is 1 sccm, N₂1 sccm gas, Ar gas
20 sccm, and further Si ₂H₆0.0002 gas
It is introduced into the vacuum chamber 1 at sccm, and the substrate temperature is 800
Film formation was performed at 30 ° C. for 30 minutes.

After the film synthesis, the film obtained on the substrate 2 was examined by infrared absorption spectroscopy and X-ray diffraction, and it was confirmed that the film was a cubic boron nitride single-phase thin film.

The composition ratio of elements in the thin film was analyzed by secondary ion gravimetric analysis, and it was found that the ratio of silicon (Si) atoms to boron (B) atoms was 400 ppm.

When the activation energy of the specific resistance and electric resistance of the obtained thin film was examined, the specific resistance was 3 × 10 ⁻¹ Ωc.
m was confirmed to be an n-type semiconductor.

Example 4 A cubic boron nitride thin film was synthesized using the same ECR plasma CVD apparatus as in Example 1.

However, in this embodiment, H ₂ S gas is used instead of SiH ₄ gas. Therefore, in this embodiment, after plasma etching, 1 sccm of B ₂ H ₆ gas, 1 sccm of N ₂ gas and ₂ sccm of Ar gas were used.
0 sccm, and 0.0005 sccm of H ₂ S gas
At a substrate temperature of 800 ° C.
Film formation was performed for 00 minutes.

After the film synthesis, the film obtained on the substrate 2 was examined by infrared absorption spectroscopy and X-ray diffraction, and it was confirmed that the film was a cubic boron nitride single-phase thin film.

The composition ratio of elements in the thin film was analyzed by secondary ion gravimetric analysis, and it was found that the ratio of sulfur (S) atoms to boron (B) atoms was 500 ppm.

When the activation energies of the specific resistance and electric resistance of the obtained thin film were examined, the specific resistance was 3 × 10 ⁻¹ Ωc.
m was confirmed to be an n-type semiconductor.

Comparative Example In a comparative example, a cubic boron nitride crystal is synthesized by a known high pressure synthesis method.

Hexagonal boron nitride (hBN) was used as a fine powder raw material, and MgBN ₃ was used as a catalyst. Silicon (Si) powder was added as an n-type impurity element at a ratio of 30 mg of Si to 1 g of the fine powder raw material when the raw material was prepared.

The cubic boron nitride crystal was slowly crystallized by setting a temperature difference in the cell under a high pressure and high temperature of 50,000 atm and about 1700 ° C. Thus, a cubic boron nitride crystal having a size of 0.5 mm was obtained.

The cubic boron nitride crystal thus obtained was examined by infrared absorption spectroscopy and X-ray diffraction.
It was confirmed to be a cubic boron nitride single-phase crystal.

The composition ratio of elements in the crystal was analyzed by the secondary ion gravimetric analysis method, and it was found that the ratio of silicon (Si) atoms to boron (B) atoms was 4000 ppm.

When the activation resistance of the specific resistance and electric resistance of the obtained crystal was examined, the specific resistance was 50 Ωcm. Thus, it was shown that the cubic boron nitride crystal obtained by the high pressure synthesis method has a very high specific resistance and is not suitable as a semiconductor.

[0069]

INDUSTRIAL APPLICABILITY In the present invention, as shown in the above-mentioned embodiments, the hydrides and halides of silicon or the hydrides and halides of sulfur which are easily available in the form of commercially available high-pressure liquid gas are used. In addition, since a mechanism for adjusting the amount of addition of the above compounds to the raw material gas in the gas phase state in the plasma CVD method can be relatively simple, cost reduction can be achieved, and high quality and large size n
A cubic boron nitride semiconductor crystal can be manufactured.
Therefore, if the present invention is used for the production of n-type cubic boron nitride semiconductor crystals, which are expected to be applied to semiconductor materials such as various tools, heat-resistant devices and environment-resistant devices, heat dissipation substrates, optical materials, acoustic diaphragms, etc. It is effective.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an ECR plasma CVD apparatus used for forming an n-type cubic boron nitride thin film in an example according to the present invention.

[Explanation of symbols]

 1 Vacuum Chamber 2 Substrate 3 Heater 4 Substrate Holder 5 High Frequency Voltage Source 6 DC Current Source 7 ECR Plasma Chamber 8 Electromagnetic Coil 10 Opening 11 Microwave

Claims (2)

[Claims] 1. A cubic is prepared by introducing a raw material gas containing a boron atom-containing gas and a nitrogen atom-containing gas as main components into a reaction system and supplying plasma generated by activation of the raw material gas to a heated substrate surface. Plasma CV for depositing crystalline boron nitride
In method D, by adding at least one of a hydride and a halide of silicon to the raw material gas in a vapor phase state,
A method for manufacturing an n-type cubic boron nitride semiconductor, comprising forming an n-type cubic boron nitride semiconductor thin film on the surface of the substrate while doping an n-type impurity element. 2. A cubic gas is prepared by introducing a raw material gas containing a boron atom-containing gas and a nitrogen atom-containing gas as main components into a reaction system and supplying plasma generated by activation of the raw material gas to a heated substrate surface. Plasma CV for depositing crystalline boron nitride
In method D, by adding at least one of a hydride and a halide of sulfur to the raw material gas in a gas phase state,
A method for producing an n-type cubic boron nitride semiconductor, comprising forming an n-type cubic boron nitride semiconductor thin film on the surface of the substrate while doping an n-type impurity element.